The present invention relates generally to implantable medical devices and more particularly to implantable medical devices having metallic components or enclosures, such as cardiac pacemakers, nerve stimulators, implantable drug dispensers, implantable defibrillators and the like.
In the context of implantable medical devices employing metallic enclosures or components, there have been numerous proposals for enhancing the biocompatibility of the surfaces of the enclosures or components. Typically, implantable electronic medical devices such as pacemakers, defibrillators, nerve stimulators or drug pumps, have enclosures fabricated of titanium or stainless steel. These enclosures are typically polished or bead blasted, as discussed in U.S. Pat. No. 5,673,473 issued to Johnson et al. In the context of other devices employing metal components, such as implantable heart valves and orthopedic prostheses, the use of porous sintered metal surfaces as disclosed in U.S. Pat. No. 4,206,516 issued to Pilliar and U.S. Pat. No. 4,101,984 issued to MacGregor is proposed. Such porous sintered surfaces are also suggested for a wide variety of other implantable devices, including artificial blood pumps, pacemaker electrodes, vascular access tubes, vascular grafts, and the like in U.S. Pat. Nos. 4,458,366 and 4,627,836, both issued to MacGregor. In these applications, the particle size is chosen to provide for an interconnected network of pores in the resulting sintered structure which are sized to permit ingrowth of soft or hard tissue, depending upon the application.
In the context of implantable pacemakers, cardioverters, defibrillators and other electronic stimulators, it has also been proposed to provide for porous, high surface area coatings such as porous sintered coatings in order to enhance the available surface area of the electrodes for enhanced electrical performance. For example, high surface area electrodes for location on electrical leads are discussed in U.S. Pat. No. 5,571,158 issued to Bolz et al, while high surface area electrodes forming a portion of the enclosure of an implantable stimulator are discussed in U.S. Pat. No. 4,602,637 issued to Elmqvist et al.
Recently, work done by Dr. Andreas Von Recum, as discussed in U.S. Pat. No. 5,011,494 and U.S. Pat. No. 4,846,834 suggests that soft tissue implant devices such as catheters, heart valves or reconstructive surgical material should be provided with a surface which has indentations or openings with bridging distances in the range of 1-4 microns, surrounded by solid surfaces having mean bridging distances in the range of 0.1-2 microns.